Thats the most plausible explanation I've heard so far. I say this because a vacuum leak would show up at all temps, unless it closes when metals expand.

I do have some lifter noise, which I've probably just grown accustomed to having owned an old audi (notorious for lifter noise). My Bentley says a little chatter is okay, so long as it goes away in a few mins, but the previous owner said he stuck to the yearly oil-change regimine, so it doesn't surprise me if my lifters are sticky.

I held on to my old audi for situations like this to use as my test subject, so maybe I'll replace the lifters there and if it still runs afterward, attempt on my 3er